Hydrogenation at low temperatures does not always lead to saturation: the case of HNCO

¹ Laboratoire Physique des Interactions Ioniques et Moléculaires, UMR 7345-CNRS, Aix-Marseille Université, 13097 Marseille Cedex 20, France
e-mail: jennifer.noble@univ-amu.fr
² LERMA-LAMAp, Université de Cergy-Pontoise, Observatoire de Paris, ENS, UPMC, UMR 8112 du CNRS, 5 mail Gay Lussac, 95000 Cergy Pontoise Cedex, France

Received: 25 November 2014
Accepted: 30 January 2015

Abstract

Context. It is generally agreed that hydrogenation reactions dominate chemistry on grain surfaces in cold, dense molecular cores, saturating the molecules present in ice mantles.

Aims. We present a study of the low temperature reactivity of solid phase isocyanic acid (HNCO) with hydrogen atoms, with the aim of elucidating its reaction network.

Methods. Fourier transform infrared spectroscopy and mass spectrometry were employed to follow the evolution of pure HNCO ice during bombardment with H atoms. Both multilayer and monolayer regimes were investigated.

Results. The hydrogenation of HNCO does not produce detectable amounts of formamide (NH₂CHO) as the major product. Experiments using deuterium reveal that deuteration of solid HNCO occurs rapidly, probably via cyclic reaction paths regenerating HNCO. Chemical desorption during these reaction cycles leads to loss of HNCO from the surface.

Conclusions. It is unlikely that significant quantities of NH₂CHO form from HNCO. In dense regions, however, deuteration of HNCO will occur. HNCO and DNCO will be introduced into the gas phase, even at low temperatures, as a result of chemical desorption.